The invention relates to a process for the separation of undesirable components, ("undesirable" hereinafter understood to refer to components that have to be removed like acid gas and other unwanted elements such as SO.sub.2 and other sulfur containing gases but also to components that will be recovered) from gaseous mixtures by scrubbing, in a first scrubbing column, with a physical absorbing agent i.e., absorbent, which agent, after absorbing the undesirable components, is then regenerated in a regenerating column and is reused in the first scrubbing column. The undesirable components released from the agent during regeneration contain small amounts of inert gas components which are then separated in a further high purity cleaning step in which the undesirable components are removed and the inert gases, still containing excess amounts of undesirable components, while being recycled to the scrubbing stage are further treated for removal of the undesirable components. Also, the invention further relates to apparatus for performing the process.
During the separation of an undesirable component, e.g. SO.sub.2, from a gas mixture, especially, a flue gas, additional inert gas components, e.g. CO.sub.2, and traces of N.sub.2 and O.sub.2 are also partially scrubbed from the gas. The SO.sub.2 separated from the flue gas must be liquefied in many instances so as to facilitate transportation, for example, to further processing facilities, such as sulfuric acid factories. This can be done only after a further separation of the residual gas released from the absorbing agent in a regenerating column, this residual gas primarily comprising SO.sub.2 and concomitantly scrubbed-out inert gas, particularly CO.sub.2 and the like. This additional separation or high-purity cleaning can be performed, for example, by distillation or adsorption, thereby making it possible both to withdraw pure SO.sub.2, while also to obtain an inert gas stream which still contains SO.sub.2.
In a distillative separation of the inert gases and of SO.sub.2 at almost atmospheric pressure wherein the head temperature of the distillation column is maintained so that it is not too low, e.g., not below -20.degree. C., it is essential to still leave a certain amount of SO.sub.2, for example 50% in the recycled inert gas stream. To reduce the recycled inerts from the distillation column, the loaded absorbent may be heated to release inerts which can then be separated from the loaded absorbent agent in a separator before the agent is conveyed to the regeneration columm to thereby directly recycle the maximum amount of inert gases. Such a system is disclosed e.g. in "Linde Reports on Science and Technology", No. 40/1985 p. 3-13.
However, when treating e.g. power plant flue gases the amount of SO.sub.2 recycled together with the total inert gas recycle stream can be as much as 50% of the SO.sub.2 contained in the flue gas. On the other hand the costs for such a separator are very high, and its effectiveness, moreover, is low since only about one-third of the concomitantly scrubbed-out inert gases can be separated.